Heat-transfer printing is commonly used to print an image on an article, such as a textile fabric. For example, a transfer sheet having a backing layer and an image transfer layer is printed with an image. The transfer sheet is brought in contact with the article to be printed, and heat and pressure are applied to the backing layer, causing the binder present in the image transfer layer to release from the backing layer and flow to the article, along with the printed image.
Typically, only a portion of the image transfer layer is printed with an image, and the remainder of the image transfer layer is blank. Nevertheless, heat and pressure applied to the backing layer causes the entire image transfer layer to flow and bind to the article. Consequently, the image printed on the article is surrounded by a field of binder, corresponding to the overall dimensions of the transfer sheet.
Various methods and transfer sheet assemblies have been proposed to limit transfer of the unimaged areas of a transfer sheet, when printing an image on an article
DeBoer et al. —U.S. Pat. No. 6,050,193 disclose printing an image on a water-soluble image receiving layer, curing the printed regions to form an oleophilic image and removing the non-imaged areas. The resulting imaging member can be used for lithographic printing.
Wagner et al. —U.S. Pat. No. 6,486,903 B1 disclose a media having a radiation curable coating thereon, which is printed with ink, and then exposed to radiation. The coating in the non-imaged areas is cured and becomes permanently bonded to the base sheet. The coating beneath the imaged areas is not polymerized and is transferred to an article by the application of heat.
Su—U.S. Pat. No. 6,124,417, Popat et al. —U.S. Pat. No. 6,080,261, U.S. Pat. No. 6,506,445 B2 and U.S. Pat. No. 6,824,839 B1 disclose a method of cold-transferring images. The image transfer sheet contains a water-activatable pressure sensitive adhesive layer and a water permeable detack layer on top of the adhesive layer. The transfer sheet is printed with a water-based ink composition, which activates the adhesive, that is, the adhesive layer becomes tacky where the ink composition has been applied. While in a tacky state, the imaged areas of the adhesive layer may be adhered to or bonded to a substrate.
Dinescu et al. —U.S. Pat. No. 8,350,880 B2 discloses a heat-transfer imaging system having an ink-receptive coating with a relatively high melting temperature. The activating ink contains a plasticizer, which lowers the melting temperature of the ink-receptive coating in the imaged areas. Only the imaged areas of the transfer sheet become adhesive under heat-transfer conditions.
Cross-linking agents may be provided in an image transfer sheet, as disclosed in Smith—U.S. Pat. No. 3,907,974. Reactive monomers, pre-polymers and/or cross-linking agents may be provided in the same or different layers of a transfer sheet. One or more of the reactive components may be blocked, rendering the composition unreactive, until such time has heat is applied to the transfer sheet. Examples of blocked isocyanate groups in image transfer sheets may be found in Devries et al. —U.S. Pat. No. 4,058,644 and Wagner et al. —U.S. Pat. No. 7,001,649 B2.
Despite the foregoing developments, shortcomings remain. Many of the technologies are limited to specific combinations of ink and binder, for example, a water-soluble image receiving layer and an ink composition capable of being cured to an oleophilic film, or a relatively high melting temperature binder, which requires an ink composition containing a plasticizer to lower the heat-transfer temperature, when printing on an article. Some of the technologies are directed to water-swellable and water-soluble adhesives, which may require additional treatments to be made washfast. Other technologies add complex processing steps, such as providing a radiation curable coating and curing the coating after an image has been printed on the transfer sheet.
Thus, there remains a need for an improved method and transfer sheet for transferring an image to an article, in which only the imaged areas are transferred, and which is compatible with conventional image transfer binders and ink receptors, as well as conventional aqueous ink compositions, introduces a minimum of additional processing steps and is washfast.